Yong-Cheol Kwon

Korea Aerospace University, QYK, Gyeonggi-do, South Korea

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Publications (5)4.5 Total impact

  • Yeh-Sun Hong · Yong-Cheol Kwon
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    ABSTRACT: Swash plate type piston pumps, when applied to electro-hydrostatic actuators, operate mostly in the mixed lubrication speed range, compensating for position control errors of actuator parts. Therefore, their hydrostatic piston shoe bearings should be designed to minimize frictional and leakage losses as well as the wear rate, which could be increased by insufficient hydrodynamic lubrication in the low speed range. In this study the influence of the balance and recess ratios of piston shoe bearings on their power losses were investigated under mixed friction conditions. The fundamental properties of piston shoe bearings tilted on a swash plate, such as the lift force, righting moment and leakage flow rate, were computed using a simplified Navier-Stoke's equation, to obtain an insight into methods of minimizing the power losses of piston shoes exposed to mixed friction. Six test models were designed with these two parameters decoupled and tested on apparatus which was developed to measure the friction force and leakage flow rate of a piston shoe in the motor speed range below 100 rpm. The tilting motion of the piston shoes could be observed in the mixed friction speed range and power losses could be reduced by increasing their resistance to external tilting moments.
    No preview · Article · Nov 2014 · International Journal of Precision Engineering and Manufacturing
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    Yong-Cheol Kwon · Yeh-Sun Hong
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    ABSTRACT: In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.
    Preview · Article · Apr 2013
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    ABSTRACT: In this paper a sharp-edged type damping orifice for an aircraft door damper were designed, where the dynamic viscosity of working fluid were assumed to change up to 400cSt. The discharge coefficient of the damping orifice were investigated by CFD analyses and experiments. In particular, the influences of orifice diameter, edge angle, flow direction and the Reynolds number were taken into consideration. Based on this, it has been deduced how high Coulomb friction forces of damper seals is to be allowed to meet the performance criterion with respect to the orifice size.
    Preview · Article · Dec 2012
  • Ji-Yoon Kim · Yong-Cheol Kwon · Yeh-Sun Hong
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    ABSTRACT: In order to provide the capsule endoscopes with active mobility in the human digestive system, a new twistable thread module mechanism which forms a neutral, right-handed or left-handed thread based on the rotating direction of the capsule is proposed in this paper. Being installed with disk-type permanent magnets, the capsule endoscope can be put into either a spiral motion or translation motion by an external permanent magnet mounted on a rotational actuator, which can also change the moving direction of the capsule by just leading it in the desired direction. In the in-vitro tests on a straight artificial tract whose properties were made similar to those of a pig’s colon, the thread module could propel the capsule as fast as 400 mm/min when the external magnetic field was rotated at 24 rpm. In order to achieve this speed, 0.6 mm thick arc-shaped wire-type blades with a curvature of 6.25 mm were used to work like helical threads. And it was also necessary that the radial and axial distance of the external magnet from the capsule were maintained at optimum values, while at the same time the rotating axes of the external magnet and the capsule were parallel to each other. To make the latter possible, a control system has been contrived, where a multi-DOF robot was employed to automatically manipulate the position and orientation of the external magnet. Using Hall-effect sensors installed inside the capsule, its position and orientation data were detected to help the manipulator compensate the parallelism and distance errors between the external permanent magnet and the capsule, in repeated cycles. The effectiveness of the control system was verified by in-vitro tests with an arcshaped curved tract, where the capsule speed was kept over 90% of its maximum.
    No preview · Article · Mar 2012 · International Journal of Precision Engineering and Manufacturing
  • Yeh-Sun Hong · Jee-Yoon Kim · Yong-Cheol Kwon · Si-Young Song
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    ABSTRACT: In order to provide the capsule endoscopes with active mobility in human digestive system, a twistable thread module mechanism is proposed in this study. The twistable thread module forms a neutral, right-handed or left-handed thread based on the rotational direction of the capsule, which is rotated by the interactions of a revolving external magnet and the disk-type permanent magnets within the capsule. The performance of the twistable thread module mechanism was evaluated by measuring the moving speed of the capsule in an artificial tract, while changing the parameters such as pitch angle, number of thread modules, rotational speed of the external magnetic field and the distance between the external magnet and capsule. It was observed that the capsule moved faster as the pitch angle or the rotation speed of the external magnet was increased. In the double thread modules case, when the pitch angle was at 35° and the external magnet rotated at 24rpm, the capsule could move as fast as 300 mm/min, which is about 60% of the ideal speed of the spiral motion, caused by the threads slip. In the triple thread modules case, although the threads slip decreased, the capsule speed did not increase as expected because of its high friction torque, that hinders the steady rotation of the capsule body. And also, the magnet distance range dropped abruptly. In a living pig’s colon, the capsule endoscope propelled by the double thread modules with the pitch angle 35° and external magnet rotating at 18rpm, moved at a speed greater than 200mm/min, which was 83% of the capsule speed as measured in the in-vitro tests. KeywordsTwistable thread module–Capsule endoscope–Alternating magnetic field–Rotating permanent magnet
    No preview · Article · Jun 2011 · International Journal of Precision Engineering and Manufacturing